1. Field of the Invention
This invention relates generally to improved uniformity in externally excited non-thermal chemical reaction systems, and, more specifically, to such systems wherein the reactant flows over workpieces disposed in a serial manner with respect to the reactant flow.
2. Description of the Prior Art
U.S. Pat. No. 4,223,048 issued to George Engle on Sept. 16, 1980 is hereby incorporated by reference as exemplary of the type of system to which the present invention is applicable. This patent is also exemplary of current state of the art in plasma reactors wherein the reactant gas or gases flow across serially arranged workpieces. Even though the system described in the cited patent represents a considerable improvement in workpiece capacity, undesirable deficiencies in uniformity occur because of the depletion of the reactant as the reactant passes down the tube over the serially-arranged workpieces. For example, in certain deposition processes, workpiece deposit thicknesses or film properties may vary by more than the desired .+-.5% from one end of the load to the other. Various attempts have been made to compensate for this variation, such as by varying gases, flow rates and pressure, which were inadequate to substantially improve the uniformity. Thus, a need existed to improve the uniformity of certain externally excited non-thermal chemical deposition or etching processes across a load of workpieces serially arranged with respect to the reactant flow.